No Brakes

[arlray19]

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When driving from Belgium to Germany on vacation, the brakes on my 1991 Mazda (US specs.) failed. I had driven about 120 miles when the brake pedal seemed hard to depress. I was almost standing while trying to stop the car. Had to use the hand brake. After stopping, water plus anti-freeze started falling from the left side (overflow bottle area) onto the ground. After about an hour, the brakes depressed okay again. Put in more water with anti-freeze and drove off the freeway to an Esso station. Car was towed to a Mazda garage in Luxembourg. Mechanic did not think it was a brake problem. We left the car with him for two weeks while we continued our vaction in a rental car. The mechanic changed the heater thermostat. He said it could be a 'heater gasket' problem, but he found no evidence of it. He test drove the car twice for about 50 miles. After I picked up the car and was heading home to Belgium from Luxembourg, the exact same problem developed after about 1/2 hour of driving, brake pedal hard to depress. Used hand brake again to stop the car. Immediately heard noises coming from under the hood. Opened up hood. Water was BOILING in the overflow bottle. The water overflowed onto the ground just like before.
Car was towed to the town near where I live. Another Mazda mechanic checked out the car. (30 years experience). Could not find any specific problem. Said there was a small leak in a gasket but not enough to cause the problem. Suggested we take the car and use it.
Is it safe to do this?
Anybody know what is causing the problem?
The car has just over 100,000 miles on it.
Thanks,
Ray

[mazdaguy]

The brake booster works off vacuum. So your losing vacuum to the brake booster somehow. Does the engine overheat? If it had a cracked cyl head coolant could get into the intake where the vacuum source is for the brake booster. Only thing i can think of unless your converter is partially clogged which could cause vacuum loss. You did'nt say how the van runs when this happens.

[arlray19]

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Thanks for the reply. When this problem happens, the brakes do not go all at once; I noticed difficulty in depressing the pedal (hard - little give), which got worse until no brakes. There is a noise under the hood - after stopping engine I can hear it. It is a boiling sound. I have failed to look at my cool/heat guage when this has happened. The van runs okay other than the brakes.
The mechanic who last looked at it said it might be a problem with the fan in the radiator - perhaps is not working or needs cleaning. He is going on vacation for a week, so I'm trying to find out as much as I can. Also. adding a block seal to seal any cracks in the block has been suggested. What do you think?
Ray

[mazdaguy]

The large vacuum hose going to the brake booster has a one-way valve so it will have brakes even if the engine shuts off for a couple push's of the brake pedal. Possibly that check valve is sticking. You have to buy the entire vacuum hose to get the one-way valve. The fan should'nt effect engine temp at highway driving since the radiator has a 60mph wind across the radiator. Check the front of the condensor for bugs though. They clog the cooling fins and restrict airflow. Also check the aux fan operation.

[arlray19]

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Again, thank you for the help. You seem very knowledgeable. The car is definitely overheating. I am hoping it is not a gasket problem as the mechanics are telling me it will cost more to change than the value of the car.
Ray